Phosphide-based nanowire for visible and near-infrared miniature photon emitters

我们将利用我们在含磷纳米线的生长、表征和器件开发方面的丰富经验，通过绿色、高效的发光二极管(LED)和激光器开发超小(直径在0.1~10微米)近红外线。这些结构可用作显示器中的红绿像素，特别是用于虚拟和增强现实的微型显示器。此外，我们将一步到位地制造双色2D发射极阵列，其成本低于目前用于微型显示器和生物传感和成像的技术。与硅相比，III-V半导体(例如GaAs)有效地将电能转化为光。它们构成了LED(固态照明)和激光(光学数据存储-DVD等和光纤系统)的基础。目前的一个挑战是为微型显示器应用生产非常小的LED(直径为10微米或更小)。此外，虽然目前的技术提供了高效率的蓝光和红光LED，但绿光LED的效率仍然明显较低。这就是所谓的“绿色鸿沟问题”。传统的LED技术使用在大晶圆上生长；使用化学蚀刻和机械切割形成单独的器件。因此，生产小型设备具有挑战性。此外，这些小型设备的表面积与体积之比很大，这会影响性能。我们的方法使用纳米线，它从最初的起始衬底垂直向上生长为非常细的线束(典型直径~100 nm)。每根纳米线可以形成一个单独的LED，因此提供了非常小的设备。在生长过程中，可以增加钝化层以减少有害的表面效应。由于纳米线和衬底之间的接触面积非常小，因此可以将非常不同的材料组合在一起，例如硅上的III-V半导体。这使得纳米线LED可以与硅驱动电子设备直接集成。纳米线还有其他几个优点。它们的小尺寸允许集成更多不同半导体的组合，特别是具有不同晶格参数的组合。对于标准LED技术，材料之间的不匹配导致的应变可能会降低器件性能。然而，对于纳米线来说，它们更高的应变容忍度提供了更多的设计参数。大多数III-V半导体可以以两种不同的晶体结构(闪锌矿或纤锌矿)中的一种存在，但对于标准生长，只有前者存在。然而，纳米线可以用纤锌矿结构生长，这种结构具有改进的电子能带结构，提供有效的绿色发射；这在闪锌矿形式下是不可能的。因此，基于含磷半导体(如AlInP)的纳米线有可能解决绿隙问题，提供与红色和蓝色LED相当的效率。由于纳米线的直径可以控制，这是决定晶体结构的一个参数，我们的目标是生长闪锌矿和纤锌矿交替结构的2D纳米线阵列。由于每种结构都发射不同波长的光，这将在单一生长步骤中提供两种颜色的2D LED阵列。目前的RGB显示器需要红色、绿色和蓝色像素分别增长，然后拾取并放置到最终显示器中，这是一个复杂而昂贵的过程。双色阵列为增强现实中的应用提供了更高的信息密度，像素尺寸低于1um的阵列在生物传感和成像方面有一系列应用。我们的方法提供了降低器件成本的可能性，因为它们是使用单一生长步骤形成的。最后，我们将在我们开发的小尺寸LED的基础上制造超小尺寸和低工作功率的可见光激光器，目标是将发射波长扩展到当前限制的635 nm以下，转向黄色和可能的绿色发射(500-565 nm)。

We will develop ultra-small (diameters in the range 0.1 ~ 10 micron) near-IR through green, high efficiency light emitting diodes (LEDs) and lasers using our significant experience in growth, characterisation and device development of phosphorus containing nanowires. These structures have applications as red-green pixels in displays, particularly micro displays for virtual and augmented reality. In addition, we will fabricate in one-growth-step, a two-colour 2D emitter array at a reduced cost than current technology for micro-displays and biological sensing and imaging.In contrast to silicon, III-V semiconductors (e.g. GaAs) efficiently convert electrical energy into light. They form the basis of LEDs (solid-state lighting) and lasers (optical data storage - DVDs etc and optical fibre systems). A current challenge is to produce very small LEDs (diameters of 10 micron or less) for applications in micro-displays. In addition, whilst current technology provides high efficiency blue and red LEDs, the efficiency of green LEDs remains significantly lower. This is known as the 'Green Gap Problem'. Traditional LED technology uses growth on large wafers; individual devices are formed using chemical etching and mechanical cleaving. Producing small devices is hence challenging. In addition, these small devices have a large surface to volume ratio that impacts performance. Our approach uses nanowires which grow as very thin strands (typical diameters ~100 nm) vertically upwards from the initial starting substrate. Each nanowire can form an individual LED, hence providing extremely small size devices. During growth, passivation layers can be added to reduce the deleterious surface effects. As the contact area between the nanowire and substrate is very small, combinations of very dissimilar materials are possible, for example a III-V semiconductor on silicon. This allows the direct integration of the nanowire LED with silicon drive electronics. Nanowires give several other advantages. Their small size allows many more combinations of different semiconductors to be integrated, especially ones with different lattice parameters. For standard LED technology, the strain due to the mismatch between materials can degrade the device performance. However for nanowires, their higher strain tolerance provides access to an increased number of design parameters. Most III-V semiconductors can exist in one of two different crystal structures (zinc blende or wurtzite) but for standard growth only the former occurs. However, nanowires can be grown with the wurtzite structure, which has a modified electronic band structure, giving efficient green emission; this is not possible with the zinc blende form. Hence, nanowires based on phosphorus containing semiconductors (e.g. AlInP) have the potential to solve the green gap problem, providing green LEDs with comparable efficiencies to red and blue ones. Because the diameter of the nanowires can be controlled, and this is one parameter determining the crystal structure, we aim to grow 2D nanowire arrays of alternating zinc blende and wurtzite structure. As each structure emits light at a different wavelength this will give a two-colour 2D array of LEDs in a single-growth-step. Current RGB displays require red, green and blue pixel separate growth, followed by picking and placement into the final display, a complex and expensive process. A two-colour array provides increased information density for applications in augmented reality and arrays with pixel sizes below 1um have a range of applications in biological sensing and imaging. Our approach offers the possibility of reduced cost devices as they are formed using a single growth step.Finally, we will build on our development of small size LEDs to fabricate ultra-small size and low operating power visible lasers, aiming to extend the emission wavelength below the current limit of 635 nm towards yellow and possibly green emission (500-565 nm).